The present invention relates to a power supply unit comprising a plurality of cells connected in series, capable of supplying electric power having relatively high output voltage and large output current, and suited as an uninterruptible power supply unit, a power supply source for electric vehicles and the like. More particularly, the present invention relates to heat radiation means and a heat radiation method for the power supply unit.
As a power supply source with high output voltage and large capacity, a power supply unit including several tens to hundreds of connected cells has been proposed. In this kind of power supply unit, plural cells are required to be closely arranged in order to enhance space efficiency. For this purpose, several to several tens of cells electrically connected in series are arranged in a row and a plurality of the rows of cells are arranged in parallel in the vertical and horizontal directions by using battery holding members.
FIG. 14 shows an example of a conventional power supply unit. In this power supply unit, battery holding members 61 made of a synthetic resin, e.g., polypropylene, and having a function of holding plural rows of cells in the horizontal direction are laminated and mutually joined by thermowelding or by using an adhesive so as to be secured. A plurality of cylindrical cells 62 are connected in series in the axial direction thereof to form the row of cells. This row of cells is accommodated in a battery holding portion 61a of the battery holding member 61. The cells 62 at the leading or trailing ends of the rows of cells are mutually connected electrically, although the connections are not shown. The synthetic resin is used as a material of the battery holding member 61 in order to prevent short-circuit between the cells 62 and to obtain high processability.
However, in the case where several tens to hundreds of cells are connected as described above, the cells disposed inside a group of batteries including a plurality of the rows of cells are exposed to stagnant heat inside because of heat transfer from adjacent batteries and the like, and the temperatures of the cells disposed inside become higher than the temperatures of the cells disposed outside. If such a temperature difference occurs among the cells in the group of batteries, variations are apt to occur among the cells in their charge/discharge characteristics. Such variations reduce the reliability of the power supply unit. In order to prevent temperature rise due to heat generation at the cells 62, a method of cooling the cells 62 has been taken, wherein a refrigerant, such as air, is passed through space portions 64 between the rows of cells.
However, in the case where a plurality of the cells are arranged continuously in the flowing direction of the refrigerant, the refrigerant absorbs heat from the cells positioned on the upstream side, and the temperature of the refrigerant rises. This temperature rise decreases the efficiency of cooling the cells positioned on the downstream side. As a result, the temperatures of the cells positioned on the downstream side become relatively higher than those of the cells positioned on the upstream side.